1) Field of the Invention
The present invention refers to an overflow tank continuously supplied with a liquid such as pure water including a partition isolating two adjacent chambers from each other, and is utilized as a passage for transferring an article from one of the two chambers to the other chamber. Such an overflow tank may be advantageously used to rinse a silicon wafer with pure water in a wafer fabrication process in which a plurality of integrated circuits is formed over a surface of the silicon wafer.
2) Description of the Related Art
As is well known, the wafer fabrication process involves steps of: washing the wafers with a solution based upon alkali, a solution based upon acid, and an organic solution for removing organic material dust and metal dust therefrom; and rinsing the wafers with a liquid such as pure water after washing the wafers with each of the solutions. For example, the washing and rinsing steps are carried out before an oxide layer formation process and after a photoetching process. Of course, the organic material dust and metal dust must be removed from the wafers because they cause defects such as short circuits, and circuit breakages in the integrated circuits formed over the wafer surface.
The washing and rinsing steps must be carried out in a closed washing space so that the wafers can be protected from dust in the atmosphere. Also, when the wafer is washed in the closed washing space with at least two different solutions, the closed washing space must be divided by a partition into two washing chambers that are isolated from each other thereby, and in which the respective different solutions are independently used. This is because it is necessary to prevent a chemical reaction between the vapors of the different solutions. For example, when the different solutions comprise an alkali-based solution and an acid-based solution, respectively, and when the wafer is washed in a commom closed washing space with said solutions, vapors from the alkali-based and acid-based solutions easily mix to produce a salt by the chemical reaction therebetween, and thus the wafers may be polluted by the salt. Thus, when the wafer is washed with different solutions, the closed space must be divided into separate washing chambers so that independent washing of the wafer with the different solutions can be carried out.
Note, the solutions are frequently heated to enhance a washing effect thereof. For example, the washing temperature of an NH.sub.4 OH solution, an HCl solution, or the like is about 80.degree. C., and the washing temperature of an H.sub.2 SO.sub.4 solution or the like and the organic solution such as a dichlorobenzene solution is about 120.degree. C. The heated solutions generate large quantities of vapor thereby emphasizing the need for isolated chambers.
Conventionally, a movable partition is used to divide the closed washing space into separate washing chambers because it is necessary to transfer the wafers from one of the washing chambers to another washing chamber. Namely, the partition is moved between a closed position in which the washing chambers are isolated from each other and an opened position so that the washing chambers are in communication with each other for transferring the wafers. The use of the movable partition results in a large and expensive wafer washing installation because a drive mechanism is necessary to operate the movable partition. Also, when the partition is opened, the vapors inevitably mix with each other.
Thus, it has been suggested that an overflow tank for rinsing the wafers with a liquid such as pure water be utilized as a passage for transferring the wafers from one of the washing chambers to another washing chamber. In particular, the overflow tank is combined with a fixed partition in such a manner that the wafers can be transferred from one of the washing chambers to the other washing chamber through the overflow tank. With this arrangement, a wafer washing installation can be smaller because no drive mechanism is necessary for the partition, and the adjacent washing chambers are always isolated from each other. Nevertheless, the conventional arrangement, in which the overflow tank is utilized as the passage for transferring the wafers, involves drawbacks which should be further eliminated for the reasons as discussed hereinafter in detail.
On the other hand, a production of a liquid crystal display, in which a fine electrode pattern is formed over a display substrate by a photoetching process, involves the same problem as mentioned above.